1. Field of the Invention
The present invention relates to a brake system comprising a master cylinder that generates brake fluid pressure by a braking operation of a driver, and an electric motor-driven slave cylinder that generates brake fluid pressure according to an electrical signal based on the braking operation of the driver.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2006-306221 discloses a brake system of the type referred to as a brake-by-wire (BBW) brake system, which converts a braking operation of a driver into an electrical signal used to operate an electric brake force generator or generating means, such as a slave cylinder, and operates a wheel cylinder by brake fluid pressure generated by the slave cylinder.
In this BBW brake system, the fluid pressure chamber of the master cylinder is in communication with the wheel cylinder through the fluid pressure chamber of the slave cylinder. When the driver depresses the brake pedal, the piston of the slave cylinder first closes a port in communication with the master cylinder in order to generate brake fluid pressure, and slightly thereafter the piston of the master cylinder closes a port in communication with a fluid reservoir in order to generate brake fluid pressure. This is because, if the above-described order is reversed, the brake fluid pressure generated by the master cylinder is transmitted to the wheel cylinder through the fluid pressure chamber of the slave cylinder before the driver sufficiently depresses the brake pedal and the slave cylinder generates brake fluid pressure, resulting in an undesirable situation in which the thus-transmitted brake fluid pressure of the master cylinder affects the control of the brake fluid pressure by the slave cylinder.
In general, a given vehicle's brake light which informs a following vehicle of the braking operation of the given vehicle is lit up when the driver depresses the brake pedal and the brake light switch turns on. However, in the conventional BBW brake system, the wheel cylinder is operated by the brake fluid pressure generated by the slave cylinder during normal system operation and the wheel cylinder is operated by the brake fluid pressure generated by the master cylinder during abnormal system operation. Therefore, if the brake light is set so as to light up at the timing at which the slave cylinder generates brake fluid pressure during normal system operation, a delay occurs in the timing at which the brake light lights up during abnormal system operation where braking is performed by the brake fluid pressure generated by the master cylinder. Conversely, if the brake light is set so as to light up at a timing at which the master cylinder generates brake fluid pressure during abnormal system operation, the brake light lights up too early during normal system operation where braking is performed by the brake fluid pressure generated by the slave cylinder.